1. Field of the Invention
The invention is directed to a fuel supply system for at least one marine diesel engine.
2. Description of the Related Art
It is known that marine diesel engines can be operated with different types of fuel. For example, it is possible to operate marine diesel engines with heavy oil fuels on the one hand and with distillate fuels on the other hand. Heavy oil fuels are economical but cause relatively high fuel emissions due to their high sulfur content. Distillate fuels cause lower exhaust gas emissions but are expensive. Marine diesel engines are operated with heavy oil fuels on the open sea for reasons of economy. On the other hand, when a ship is to be operated in proximity to a coast, in a so-called SECA (Sulfur Emission Control Area) zone, operation of the marine diesel engine must be switched over from a heavy oil fuel to a distillate fuel for reasons pertaining to emissions. A ship may only enter a SECA zone when a marine diesel engine meets the emission requirements of this SECA zone with respect to harmful emissions by burning a distillate fuel.
Conventionally, a fuel supply system for a marine diesel engine by means of which the marine diesel engine can be supplied either with a heavy oil fuel or with a distillate fuel has what are known as a feeder fuel circuit and a booster fuel circuit.
Either the first fuel or the second fuel can be conveyed via the feeder fuel circuit in the direction of a mixing tank by a first pump device. By a second pump device of the booster fuel circuit, fuel can be conveyed from the mixing tank in the direction of the marine diesel engine or every marine diesel engine. The first pump device of the feeder fuel circuit sucks in the respective fuel with a first conveyed volume flow. A first partial conveyed volume flow of this first conveyed volume flow is conveyed in direction of the mixing tank, and a second partial conveyed volume flow of this first conveyed volume flow is circulated in the feeder fuel circuit. The second pump device of the booster fuel circuit sucks the fuel out of the mixing tank with a second conveyed volume flow, which is appreciably larger than the first conveyed volume flow. Thus, more fuel is conveyed via the marine diesel engine or every marine diesel engine than is actually consumed so as to make surplus fuel available particularly for cooling and lubrication. Fuel that is not consumed by the internal combustion engine(s) is returned to the mixing tank via a feed flow of the booster fuel circuit.
It is known to arrange an individual coarse filter, respectively, in the booster fuel circuit upstream of the marine diesel engine or every marine diesel engine in order to filter coarse impurities from the fuel conveyed in direction of the respective marine diesel engine by the booster fuel circuit. Filters of this kind are also known as control filters. Further, it is known from practice to provide a fine filter in the feeder fuel circuit to filter fine impurities from the fuel conveyed into the mixing tank by the feeder fuel circuit.